Generic rearview mirrors on the one hand serve to observe the traffic behind and on the other hand as signaling mechanism to give the driver and/or other passengers and/or other drivers warning signals or reference signals. There the signaling occurs by sending out light signals, whereby light-emitting lighting means are arranged behind the reflective element serving to show the traffic behind.
So that the light signals of the signaling mechanism can be viewed by the observer on the front side of the reflective element, the reflective element is designed partly transparent. Such partly transparent reflective elements are also designated as so-called Venetian mirrors.
A generic rearview mirror is described for example in U.S. Pat. No. 6,045,243. In this rearview mirror a polarizing film is arranged between the lighting means and the reflective element, with which the light radiated by the lighting means can be deflected in a predominant direction. The result of this is that when the front side of the reflective element is viewed the illumination strength depends on the viewing angle relative to the predominant direction when the signaling mechanism is switched on. If the driver receives a warning for example, a predominant direction is selected, in which the signaling mechanism can be viewed clearly from the driving position alone. The warning signal cannot be viewed from the viewing direction of the traffic behind or to the side, since the light emitted by the lighting means is shaded in this direction by the polarizing film.
The disadvantage of the mirror described in U.S. Pat. No. 6,045,243 is that the polarizing film weakens the light overall, so that a relatively high density of light is required to ensure adequate illumination strength on the front side of the reflective element. This high light output in turn requires a relatively high electric power supply and causes high heat losses.